Second law of thermo on a macroscopic scale

Thermodynamics makes good predictions for macroscopic experiments, but the actual physics is going on in the microscopic particular level.

The second law of thermo is often thrown around, usually by people who couldn't explain F=ma back to you.

My question is the way the second law used on the macroscopic scale ever relevant? I mean can it ever be used in a context where the mechanism for it's action is not on the microscopic particular level?

Your thinking is kind of confusing. Initially, thermodynamics was worked out on macroscopic scales, so it must have been relevant. Later, the microscopic aspects (e.g. quantum states) were worked out and supported the macroscopic results. This is why it's such a successful theory.